In information industry, electrostatics has been a troublesome problem in the production of numbers of electronic components. Electrostatics, generated during the production process of electronic products, may draw dust or other pollutants that might damage the properties of the products. Also, modern electric devices are highly sensitive to electrostatics, so that temporary or permanent damage of such devices by electrostatics has been increasingly reported.
Nowadays, liquid crystal display (LCD) is widely used in various fields producing notebook computer, monitor, TV, etc, due to its potential for weight reduction and slimness.
In general, LCD consists of liquid crystal cell containing liquefied crystal therein, polarizer, and pressure sensitive adhesive layer for the adhesion of the above liquid crystal and the polarizer. The polarizer consists of multilayer including a row of iodine compounds or dichroic polarizing material, protective film, such as triacetyl cellulose (TAC), to protect polarizing element, pressure sensitive adhesive layer, and releasing film, etc.
Particularly, the production of LCD includes the process of adhering polarizer, during which static electricity is generated after peeling releasing film out of pressure sensitive adhesive layer. The generated static electricity affects orientation of liquid crystal in LCD, resulting in defectives.
In order to prevent generation of static electricity as explained above, a method of forming anti-static layer on an exterior surface of polarizer was proposed, but the effect was not good enough, and could not prevent generation of static electricity basically. Therefore, the anti-static function is needed for the pressure sensitive adhesive to prevent generation of static electricity completely.
Conventional methods for providing the anti-static function of the pressure sensitive adhesive include a method of adding conductive components such as conductive metal powder or carbon particle, or a method of adding an ionic material such as a surfactant type. However, the method of adding metal powder or carbon particle had a disadvantage that transparency of the pressure sensitive adhesive layer is decreased since a large amount of metal powder or carbon particle should be used to provide the anti-static function. Also, the method of adding a surfactant had disadvantages that it is vulnerable to humidity, and adhesive property is decreased due to the migration of surfactant to a surface of the pressure sensitive adhesive.
Japanese Patent Publication No. 1993-140519 discloses a method for preventing generation of static electricity by adding plasticizer of ethyleneoxide-modified phtalic acid dioctyl in the pressure sensitive adhesive. However, the addition of such plasticizer only cannot prevent the fundamental generation of static electricity and not to eliminate static electricity remaining after the separation of releasing film, either.
Also, Japanese Patent Publication No. 1994-128539 discloses a method for providing anti-static property by mixing polyether polyol compounds and one or more alkali metal salts. However, this method has disadvantages that the use of polyether polyol compounds may affect the degree of crosslinking. To avoid such affection on the crosslinking degree, the inventors of the above patent tried to make crosslinking first by using isocyanate crosslinking agent, and then dissolved the composition again before mixing process of the polyether polyol compound and the alkali metallic salt. However, such processes are very difficult to be applied in real industry.
Therefore, it is required to develop a pressure sensitive adhesive having excellent antistatic property without changing compatibility and durability.